All types of unconventional/exotic computing. I think this has been criminally neglected ever since the ascendancy of the von neumann architecture digital computer.

1) The Zen of Exotic Computing by Peter Kogge - https://epubs.siam.org/doi/10.1137/1.9781611977295

2) Handbook Of Unconventional Computing in 2-vols (Vol1-Theory, Vol2- Implementations) by Andrew Adamatzky et al. - https://www.worldscientific.com/worldscibooks/10.1142/12232#...

Related: OSes based on persistent memory. As in: main RAM persists across reboots, distinction RAM <-> storage goes away, saving files & the whole concept of memory-mapped files can be tossed, code of any executable is always ready to jump to, etc.